1. Reliability of SNS Superconducting Linac April 12, 2011 Jeff Saunders SNS/ORNL

2. 2Managed by UT-Battelle for the U.S. Department of Energy MSU Visit., July 23, 2010 SNS LINAC Twenty-three cryomodules – 11 medium beta cryomodules – 12 high beta cryomodules – 9 empty slots for high beta cryomodules

3. 3Managed by UT-Battelle for the U.S. Department of Energy MSU Visit., July 23, 2010 Machine Availability Optimization Strategy is to minimize downtime by recognizing nuisance failures and permitting continued operations Many component failures create no downtime due to redundancy or operational strategy Machine interlocks allow bypassing non-critical failed components and controlling operations via redundant components until repairable during scheduled maintenance period Proactive maintenance program repairs or replaces weak components prior to failure minimizing impact on reliability

4. 4Managed by UT-Battelle for the U.S. Department of Energy MSU Visit., July 23, 2010 Most Frequent Maintenance / Repair Activities Pressure Transducers Cold Cathode Gages Tuner – Piezo / Harmonic Drive HOM Issues Helium Circuit / Beam line Vacuum Leaks Loose RF Cable

5. 5Managed by UT-Battelle for the U.S. Department of Energy MSU Visit., July 23, 2010

6. 6Managed by UT-Battelle for the U.S. Department of Energy MSU Visit., July 23, 2010 Pressure Transducers Multiple incidents of PT failures (35 – 40) PT’s are located on surge tank and return piping Component electronics failures due to radiation damage Failure is considered a nuisance failure and not a reliability issue Replacement transducers have had much better service life.

7. 7Managed by UT-Battelle for the U.S. Department of Energy MSU Visit., July 23, 2010 Cold Cathode Gages Two types of CCG on the existing CM. They are located on the Insulating Vacuum and on the Fundamental Power Coupler (FPC) CCG failure in the insulating vacuum are considered a nuisance failure and does not affect machine reliability FPC cold cathode gauges, provide interlock signals for window protection, proved to be troublesome and unreliable in operation, often with an erratic signal character. Operational input is being transitioned from CCG to electron probe interlock for RF window protection

8. 8Managed by UT-Battelle for the U.S. Department of Energy MSU Visit., July 23, 2010 Tuner Pressure fluctuations, 2-4-2K transition, component installation issues, and component manufacturing issues  about 14 tuners have been repaired. – Harmonic driver, piezo stack and/or motor failure – Worn out in progress, loosen connection, slips; unstable mechanical boundary; irregular detuning Piezo Actuator (2X) Flexure Connection to Cavity (2X) Flexure Connection to Helium Vessel Motor & Harmonic Drive Connection to Helium Vessel

9. 9Managed by UT-Battelle for the U.S. Department of Energy MSU Visit., July 23, 2010 Failed piezo at tuner end

10. 10Managed by UT-Battelle for the U.S. Department of Energy MSU Visit., July 23, 2010 Failed piezo base

11. 11Managed by UT-Battelle for the U.S. Department of Energy MSU Visit., July 23, 2010 Harmonic Drive Components

12. 12Managed by UT-Battelle for the U.S. Department of Energy MSU Visit., July 23, 2010 Harmonic Drive operating principle

13. 13Managed by UT-Battelle for the U.S. Department of Energy MSU Visit., July 23, 2010 Harmonic Drive Operating Principle

14. 14Managed by UT-Battelle for the U.S. Department of Energy MSU Visit., July 23, 2010

15. 15Managed by UT-Battelle for the U.S. Department of Energy MSU Visit., July 23, 2010

16. 16Managed by UT-Battelle for the U.S. Department of Energy MSU Visit., July 23, 2010 HOM coupler issues – Introduced to avoid beam break-up and cavity heating from high order mode (very small probability) – Some cases showed excessive fundamental power coupling and attenuator damage – 6 HOMs feed throughs have been removed from 2 CM

17. 17Managed by UT-Battelle for the U.S. Department of Energy MSU Visit., July 23, 2010 HOM in SNS SNS HOM history Beam breakup & instability; no issue HOM power is the main reason for SNS to have HOM coupler (but chance is very small) More realistic analysis with actual frequency distributions measured. Probabilities for hitting dangerous beam spectral lines are much less. Future concerns HOM feedthroughs will be taken out as needed Spare cryomodule Does not have HOM feedthroughs for cavities PUP cryomodule Will not have HOM couplers for new cavities

18. 18Managed by UT-Battelle for the U.S. Department of Energy MSU Visit., July 23, 2010 Helium Circuit and Beamline Leaks Predominately ceramic feed throughs in end cans – Multiple have been replaced – Spare and PUP CM end cans will not use these ceramic feedthroughs HOM ceramic feed throughs have also been an issue – Spare and PUP CMs eliminate the HOM ceramic feedthrough Also experienced one end dish to helium tank weld leak

19. 19Managed by UT-Battelle for the U.S. Department of Energy MSU Visit., July 23, 2010 CM23 Repair Leak in the weld between the NbTi end dish and the Ti Helium vessel. Was repaired in the Front End building by SNS personnel.

20. 20Managed by UT-Battelle for the U.S. Department of Energy MSU Visit., July 23, 2010 Loose RF Cable Two incidences of loose RF cable impacting operations Cryomodule warm-up procedure now includes step verifying cable tightness

21. 21Managed by UT-Battelle for the U.S. Department of Energy MSU Visit., July 23, 2010 SNS SCL, Operations and Performance We have learned a lot in the last 6 years about operation of pulsed SC linacs: – Operating temperature, Heating by electron loadings (cavity, FPC, beam pipes), Multipacting & Turn-on difficulties, HOM coupler issues, RF Control, Tuner issues, Beam loss, interlocks/MPS, alarms, monitoring, … Current operating parameters are providing very stable and reliable SCL operation – Less than one trip of the SCL per day mainly by errant beam or control noise Proactive maintenance strategy (fix annoyances/problems before they limit performance) Several cryomodules were successfully repaired without disassembly – Multiple beam-line repairs were successfully performed

22. 22Managed by UT-Battelle for the U.S. Department of Energy MSU Visit., July 23, 2010 Thank you for your attention!